Vacuum pumps are known which are oil-free in their vacuum chambers and which are therefore useful in clean environments such as those found in the semiconductor industry. In such a manufacturing environment, if lubricants were present in the vacuum chambers, these materials could potentially back migrate into the process chamber and, in so doing, may cause contamination of the product being manufactured. Such dry vacuum pumps are commonly multi-stage positive displacement pumps employing intermeshing rotors in each vacuum chamber. The rotors may have the same type of profile in each chamber or the profile may change from chamber to chamber.
In either a Roots or Northey (“claw”) type device, each chamber is typically formed from two separate machined stator components with the rotor components being located in the cavity formed there between. It is necessary to provide a sealing means between the two stator components in order to prevent leakage of the process gas from the pump and to prevent any ambient air from entering the pump. An o-ring is typically provided to perform this sealing function. However, given the harsh corrosive nature of the process gases these o-rings are readily attacked and need to be replaced frequently, thus causing costly servicing down times for the entire process. Furthermore, the contact surfaces of the stator can experience corrosion, which can lead to anomalies in these surfaces such that distortion of the pump case can occur. This distortion leads to a reduction in clearance between rotating and static components that, in turn, can affect the mechanical reliability of the pump.
Conventional systems are known which introduce mechanical barriers to protect the static sealing mechanism by preventing some of the hazardous/corrosive gaseous material from reaching the o-ring component. However, compatibility must be achieved between the material chosen to form this mechanical barrier and the process gas. Furthermore, additional complexity is introduced into the system by the presence of such a mechanical barrier and such a mechanical barrier will not generally protect the contact faces of the stators.
The present invention aims at overcoming the aforementioned problems by providing an alternative, simple means for protecting the sealing mechanism and the contacting stator faces.